(1) Field of the Invention
The present invention relates to a process for preparing a halogenated benzene derivative by halogenating benzene and/or a benzene derivative in the presence of a zeolite as the catalyst. More particularly, the present invention relates to a process for selectively preparing a p-substituted halogenated benzene derivative by halogenating benzene and/or a benzene derivative, which is characterized in that a zeolite modified with a metal salt is used as a catalyst.
(2) Description of the Related Art
Halogenated benzene derivatives, especially di-substituted halogenated benzene derivatives, are industrially important as intermediate compounds for the production of various compounds. A di-substituted halogenated benzene derivative includes three isomers, that is, ortho-, meta-, and para-isomers, and p-substituted halogenated benzene derivatives are especially important for the production of various organic compounds. Paradichlorobenzene (hereinafter referred to as PDCB), which is a p-substituted halogenated benzene derivative, is used as a starting material in medicines and agricultural chemicals and is directly used as an insecticide or deodorizer, and hence, this compound is very valuable from an industrial viewpoint.
At the present, dichlorobenzene (hereinafter referred to as DCB) is industrially prepared by blowing chlorine into benzene or monochlorobenzene (hereinafter referred to as MCB) in the presence of a Lewis acid catalyst such as ferric chloride or aluminum chloride to effect chlorination. DCB prepared according to this process comprises 30 to 40% of the ortho-isomer, about 5% of the meta-isomer, and 60 to 70% of the para-isomer, and it is difficult to make any great change in this formation ratio in these three isomers.
Various research works have been carried out with a view to improving the selectivity to the paraisomer in the above-mentioned process. For example, there can be mentioned a method using a zeolite as the catalyst. More specifically, Journal of Catalysis, 60, pages 110-120 (1979) teaches that, if various ion-exchanged X-type or Y-type zeolites are used as the catalyst for the liquid phase bromination of a halogenated benzene, the para-isomer can be formed at a much higher selectivity than the selectivity attained in the conventional method using a Lewis acid as the catalyst. Furthermore, Japanese Unexamined Patent Publication No. 59-163,329 teaches that, if zeolite L is used for the liquid phase nuclear halogenation of benzenes, p-dihalogenated benznes can be prepared at a high selectivity. In connection with the gas phase halogenation, it is known that PDCB is obtained at a higher selectivity than the selectivity attainable in the conventional process if MCB is chlorinated by using a catalyst consisting of a zeolite having a pore size of 5 to 13 angstrom, such as molecular sieve 5A, 10X or 13X or zeolite HY (see Japanese Unexamined Patent Publication No. 57-77,631).
It is now considered that the demand for p-substituted halogenated benzene derivatives among di-substituted halogenated benzene derivatives will vigorously increase in the future. Accordingly, it is very important from the industrial viewpoint to selectively produce a p-substituted halogenated benzene while controlling the ratios of o-substituted and m-substituted halogenated benzene derivatives, formed as by-products, to levels as low as possible.
As pointed out above, in the selective production of p-substituted halogenated benzene derivatives by the halogenation of benzene or benzene derivatives, methods using zeolites as the catalyst are effective over the conventional methods. However, all of the known methods using zeolites are still insufficient from the industrial viewpoint because the selectivity to di-substituted halogenated benzene derivatives is not satisfactory.